Keywords: Genetic variations; Index score and genotype.
Introduction
Crop improvement techniques remain a major concern to plant
breeders to address world food shortage. Several factors such as climate,
weather, soil, edaphic and biological and more importantly crop
genotype affect crop improvement for specific or general environment
performance [1,2]. Crop genotype includes different crop forms of
inbred or pure lines hybrids, landraces, wildraces germplasm accessions,
cultivars or varieties [3,4]. These crop genotypes have diverse and wide
origin and genetic background known as genetic diversity. Genetic
diversity study is a major turnaround in understanding intra-specie
crop performance leading to crop improvement. Information of crop
performance in genetic diverse population reveals the real differences
in the nature of genetic materials used.

Metroglyph Analysis
This is a semigraphic method of studying variability in a large
number of germplasm lines taken at a time. This technique was
developed by Anderson [5] to investigate the pattern of morphological
variation in crop species.
The semi graphic method consists of the following steps.

Plotting of glyph on the graph

program should be chosen from different groups representing wide
genetic variability.

D2 statistics
The concept of D2 statistics was originally developed by
Mahalanobis [6]. Genetic diversity arises due to geographic separation
or due to genetic barriers to cross ability.
The selected genotypes are evaluated in replicated field trial and
observations are recorded on various quantitative characters.
First variances for various characters and co-variances for their
combinations are estimated.
(a) Computation of D2 values and testing their significance against
the table value of χ2 for p degrees of freedom, where p is the total
number of characters. If the calculated value of D2 is higher than table
value of χ2 it is considered significant and vice versa.
(b) Finding out the contribution of individual character towards
total divergence.
(c) Grouping of different genotypes into various clusters
(d) Estimation of average distance at (a) intra-cluster and (b) intercluster levels and
(e) Construction of cluster diagram

A small circle by which the position of a genotype or line is
represented on the graph is called glyph. For plotting of glyph on the
graph two characters having high variability are chosen. One of them is
used on the X- axis and the other on the Y-axis. The mean values of X
for each genotype are plotted on the graph against the mean values of
Y. Thus each line occupies a definite position on the graph called glyph.

In D2 analysis, a diagram is constructed with the help of D2 values
which is known as cluster diagram. The square roots of average intra
and inter cluster D2 values are used in the construction of cluster
diagram. This diagram provides information on the following aspects.

Depiction of variation

2. The distance between two clusters is the measure of the degree
of diversification. The greater the distance between two clusters the
greater the divergence and vice versa.

Variation for remaining characters of each genotype is displayed
on the respective glyph by rays. Each character occupies a definite ray
position. Variation for each character is depicted by the length of ray.
Thus, the length of ray for a particular character on the glyph may be
short or medium or long depending on the index value of a genotype.

Construction of index score

1. The number of clusters represent the number of groups in which
a population can be classified on the basis of D2 analysis

The genotypes falling in the same cluster are more closely related
than those belonging to another cluster.
References
1. Kumar M (2013) Crop Plants and Abiotic Stresses. J Biomol Res Ther 3: e125.

For this purpose, the variation for each character is divided into
three groups, viz., low, medium and high. The genotypes with low,
medium and high values are given index score 1, 2 and 3, respectively.
The worth of a genotype is calculated by adding the index values of
all the characters. Thus, the maximum and minimum score of an
individual will be 3n and n respectively, where n is the total number of
characters included in the study.

Received April 16, 2014; Accepted April 19, 2014; Published April 27, 2014

The X- and Y-axes are divided into three groups, viz., low, medium
and high. The maximum number of groups or clusters will be nine. The
variation is analyzed for various traits within the group and between
the groups. The genotypes for use as parents in the hybridization